We can (and probably should) assume that all greys generated by the program are always weak and their PA never goes over 30. However, there are some exceptions. My proposal is to make the experiment yourself. Start a new season with AC Milan, Inter or any high-level club (attention! This does not work in all clubs). Then:
1.Arrange a friendly between your reserve team and U-18 one in about 2 weeks time.
2.Mark all your reserves with Ctrl+A.
3.Get them all to U-18 OR to your first squad.
4.Continue the game.
5.In one or two days your reserves should be full of grey players again.
6.All of them will be great footballers.
7.Sign contracts with them and move them to the first team.
8.Press continue.
9.Reserves will be filled with the grey ones for yet another time…
… and you can do it forever. You can sign new genius players as long as you want. The game would be boring without all those bugs, eh?